Quality and durability are important factors in the design of systems for providing electrical connections, especially such systems utilized in the telecommunications and automotive industries. One criterion affecting the quality of such connections is the extent of effective electrical insulation surrounding the connection. Another important criterion is the maintenance of the connection in a moisture free environment. The invasion of water at the connection site is detrimental in several respects. For example, the "noise," "static" and "cross-talk" which frequently plague telecommunication systems are sometimes caused by signal leakage due to moisture at the connection site. The intrusion of water also has the obvious disadvantage of fostering corrosion and thus negatively impacting on the durability of the connection.
It is also desirable that electrical connections possess the ability to remain in a moisture free, non-corrosive environment when subjected to externally applied shock, vibration and temperature stresses.
While noise resistance, durability and moisture resistance in the face of environmental variations and other stresses is desirable in nearly all electrical connecting devices, there are also many commercial and military applications which require that electrical connections be repaired and/or modified in the field. It is highly desirable that such repair and/or modification be accomplished in the shortest period of time, in an economically efficient fashion and with a minimum of inconvenience to the field craftsperson or technician. In fact, such characteristics are also highly desirable from the standpoint of the initial manufacture of the electrical connecting device.
Nevertheless, many prior art devices and the sealant compositions used therein possess the disadvantage of being time consuming and inconvenient to manufacture and repair. For example, U.S. Pat. No. 3,897,129--Ferrar is directed to an apparatus for protecting electrical contacts by covering the contacts with a grease filled container. When repair or replacement of the connection requires reentry to the sealed contact, the container is removed from the contact. Disadvantageously, however, grease remains coated on the contact. This grease must be removed before the repair and/or modification can be effected, an undesirably messy and time-consuming task. Furthermore, the container must be refilled with grease prior to completion of the repair work.
It is also known to encapsulate electrical contacts within a container by means of a two-part liquid composition. When mixed together, the two components react slowly to produce a hard, relatively inflexible material. Before the ingredients set, the mixture is poured into the container where it cures in situ to form a hard, rigid plastic. U.S. Pat. Nos. 4,375,521--Arnold and 4,102,716--Graves disclose such devices. The procedure required by these devices, however, involves the obviously undesirable requirement that the composition be prepared under the conditions existing at the field location, thereby delaying and affecting the quality of the repair and/or modification. Moreover, the physical characteristics of the cured material are such that access to the actual contact is inhibited. Additionally, the chemical curing reaction is controlled by the ambient temperature, proceeding slowly or incompletely at low temperature and being inconveniently rapid at high temperatures.
Applicants have noted a failure of the prior art to provide devices and compositions which overcome the disadvantages described above while maintaining the stringent requirements of noise, moisture and temperature cycling resistance and environmental benignity and stability. Applicants have discovered novel polymer containing compositions which satisfy the long-demanded need for materials possessing this set of desirable characteristics.
Certain organic polymers are known to exhibit unique combinations of properties. Among these are block copolymers composed of polymer chains comprised of at least two different types of polymeric units, in which sequences (blocks) of one type of polymeric unit alternate with sequences of another type. If combined with the proper polymeric architecture, the resulting polymeric materials exhibit properties distinct and superior to those of each individual repeating component. For example, it is known that certain performance profiles such as heat resistance, thermoplasticity and elastomeric properties which are not attainable singly or in combination with homopolymers or even with random copolymers are attainable with such block copolymers or combinations thereof.
U.S. Pat. No. 3,265,765--Holden et al describes thermoplastic elastomers comprising block copolymers of the A-B-A configuration. Each A block is a glassy or resinous non-elastomeric thermoplastic polymer sequence and each B block is an elastomeric polymer block of a conjugated diene having a glass transition temperature considerably below the glass transition temperature of block A.
U.S. Pat. No. 4,942,270 to Gamarra is said to be directed to providing heat resistant gels without the necessity of using electron beam radiation. The compositions of Gamarra are poly(styrene-ethylene-butylene-styrene triblock copolymer-oil compositions. The compositions contain about 2 to about 30 parts by weight of a triblock copolymer and about 70 to about 98 parts by weight of a plasticizer. Polybutene oil and paraffinic/naphthenic oils or mixtures of these oils are disclosed as examples of plasticizer.
Preparation of the Gamarra compositions requires high temperature melt blending or high shear blending at lower temperatures. The need for high temperature/high shear blending of the Gamarra compositions is an obvious disadvantage in the preparation of these compounds. Another significant disadvantage of the Gamarra compositions is that such compositions are described as being nonmeltable. That is, these compositions will degrade, decompose or break down in some manner before they reach a temperature at which the composition will melt and become pourable. This is a disadvantage in the manufacture of sealed electrical connectors because of limited process flexibility. Furthermore, the repair or replacement of sealed electrical connectors containing such compositions would also be hampered by such characteristics.
Shell Chemical Company Technical Bulletin SC:759-85 provides technical information on KRATON G 1701, a diblock copolymer. This bulletin indicates that KRATON G 1701 is compatible with KRATON G 1652, a triblock copolymer, and that blends of the two polymers can be formulated to provide sealants with lower cohesive strength than KRATON G 1652 alone. The use of such materials in electrical connectors is not suggested nor is the means to provide permanently non-volatile formulations suggested.
The use of KRATON G Rubbers in clear sealants is presented in a July 1987 Shell Chemical Company Technical Bulletin entitled "KRATON G Rubbers in Clear Sealants." This report indicates that diblock copolymers such as KRATON G 1701x provide a means to tailor the adhesion and cohesive strength of a sealant composition. The diblock copolymer KRATON G 1701x is also said to provide unique thixotropic characteristics to sealant compositions. The sealants disclosed in this bulletin are intended to be used in sealing material such as glass, metal or wood from the effects of the environment. These clear sealants are said to adhere to a variety of substrates and may be painted if desired after the solvent components have evaporated. Means to provide 100% non-volatile compounds are not disclosed, such compounds being essential for sealing electrical connectors.
The use of KRATON Thermoplastic Rubbers in oil gels is presented in Shell Chemical Company Technical Bulletin SC:1102-89 of April 1989 entitled "KRATON Thermoplastic Rubbers in Oil Gels." This bulletin provides information on the physical properties of KRATON G 1651 and KRATON G 1701x. The bulletin indicates that the KRATON G rubber compounds may be used in a blend with polyethylene wax and processing oil to use as a waterproof sealant for telecommunications cable. The need for temperature resistance, insulation resistance and other qualities required for sealed electrical connectors are not discussed.